In most manufacturing processes, it is necessary to convey an article from one station where one part of the process is performed to another station where another part of the process is performed. The ability to convey the articles automatically and in a timed sequence can often mean the savings of large sums of money and large amounts of time. Furthermore, it is often necessary not only to convey an article from one station to a second station, but also to accurately position the article at the second station. There is also the need to perform operations on articles at one station along the conveyor and then, with minimal delay or article repositioning, to convey the article to a further station with the same conveyor.
The above listed objectives are also desirable in the handling of printed circuit boards. Ideally, printed circuit boards have an overall rectangular shape, have a relatively thin cross sectional thickness, and are flat. However, in reality circuit boards are often warped and are not manufactured to precise tolerances in any of the three dimensions. Therefore, any conveying system must accomodate these realities.
Prior art conveyors for conveying printed circuit boards have included belt conveyors, pushing or pulling devices, chain conveyors and vibration conveyors. Belt conveyors have the disadvantage of not permitting work to be done on the underside of the conveyed board. Furthermore, belt conveyors take up greater space since provision has to be made for the belt return. It is also difficult to get clinch heads in their proper alignment. In one type of belt conveyor, two relatively thin belts are used to engage the boards on each side. However, it is difficult to keep the boards aligned and misalignment and jamming often occurr. Jamming particularly occurrs when alignment guides are used on either side of the belts. Link chain conveyors which carried the boards on projections have difficulties with bearings and pins wearing out and in addition tend to create an oily environment resulting in oil getting on the cards. Pushing and pulling devices also suffer from the inability to locate the cards accurately and further have the disadvantages of being expensive and prone to breaking down. In one known type of vibrator conveyor, a large number of upstanding, vibrated bristles are used to convey the board. This type of conveyor not only has the disadvantages of larger space requirements and the inability to allow work to be done on the underside of the card, but also tends to build up static electricity on the board.
Conveying a flat pan or circuit board with a rotary member such as a roller drive is known in the prior art. Such devices are disclosed in the Del Bianco et al U.S. Pat. Nos. 4,377,434 and Perkey U.S. Pat. No. 746,145, and a Russian Patent No. 186,370. In particular, the Del Bianco et al patent discloses a V-shaped roller drive that includes an array of opposed roller elements 92, each element having a slot and a driving surface disposed at the base of the slot. Thus, this patent discloses the coveyance of a circuit board through the physical engagement of the edge of the board with a driving surface at the base of the roller element slot. The Perky patent discloses a roller type conveyor for conveying pans wherein the top and bottom flanges of the rollers engage the top and bottom surface edges of the pan. A spring forces the two flanges against the pan to ensure positive drive. The Russian patent discloses a conveying system for film material in which opposed rollers with V-grooves are spaced apart a distance that is less than the width of the film. Thus, the film is bowed when engaged by the opposed rollers. Consequently, in each of these patent references, the conveyance of the article requires a forced contact between the opposed rollers and the article to be conveyed.
The disadvantages of the roller conveyors disclosed in the aforementioned patents include possible jamming by warped or oversized articles, a positive drive that can defeat positioning of the conveyed article, and wearing on the conveyed article and the conveyor rollers.